Ah, the Advanced RB!
This book is almost a must-buy, as it VASTLY adds to the core book's world-fluff, almost doubling the info available.
It also adds new mechanics, allowing PCs to become more powerful - or just more interesting - but at a unique cost…
It also has a number of new adventures, as well as ways to customize one's PC to a much higher degree.
[5 of 5 Stars!]